This disclosure concerns drain valves in which fluid can flow down a drain under the action of gravity. More particularly, this disclosure concerns drain valves for location in a liquid outflow from a urinal, sink, floor drain or the like. Open gravity drains allow escape of odorous gas or vapor into the surrounding air. Furthermore, they can expose individuals to airborne contaminants or, in the case of back-flow, water-borne contaminants, thereby increasing the risk of infection and potential disease transmission. It is a known fact that urine is highly corrosive and if not flushed periodically with water, it can corrode drain pipes.
In a conventional open drain, without a trap such as a urinal or floor/ground drain, it is customary to flush the drain with water and/or a cleaning solution regularly in order to prevent the above problems. However, this consumes significant volumes of liquid, which represents an inefficient and wasteful use of available water resources.
In the event that an open drain is flushed or washed less regularly, the drain can become unsanitary and the odor emanating from the drain can attract unwanted insects and vermin to its vicinity. More recent trends towards chemical or ‘dry’ cleaning mean that the drain is more susceptible to debris retention and clogging. In the event that a drain trap is used, clogging is particularly problematic and can quickly block the drain.
In order to help maintain the sanitary nature of a drain and prevent escaping odor, there have been proposed a number of devices for insertion into the drain opening within the prior art. Certain examples propose the use of chemical holder within the urinal and open drain. However, such examples are typically bulky, such that they are not well suited to a retro-fit of existing drains, as well as being expensive to manufacture. The use of chemicals means that the device requires frequent replacement, such that the ongoing cost to an end user is significant. Also, the chemical is a known pollutant and so the disposal of the chemical within such devices represents a major and costly undertaking at the water reclamation center.
Other examples of prior art devices comprise simpler valves, which are intended to remain closed when at rest, so as to prevent escape of gas from within the drain, but which open to allow liquid flow down the drain.
Other types of valve members that may be used including sheath valves or a hinged, flapper valve. Duckbill valves may offer a further alternative in this context. However, the available static flow area of those valves and the weight of liquid required to actuate the valve member into its open condition cause potential problems. For example, a volume liquid may be retained above the valve member for extended periods of time, which can in itself be odorous or otherwise unsanitary. In some instances solids like cigarettes butts, tooth picks, mop strings and sand can catch on the hinge member causing the valve to stay in the open position for long period of time.
Furthermore, the maximum flow rate permitted through the above examples of prior art valves is limited by the valve design and construction and may be insufficient to accommodate rapid flushing do to its narrow valve inside opening or, particularly in the case of ground drains, flooding.
The inventor has also found that the provision of a mechanical valve at a drain opening can cause further problems. More specifically, the movement of fluid within a drain system can cause pneumatic pressure within the drain and, in the case of drain backflow, hydraulic pressure at the drain opening. For an open drain, this pressure would naturally be relieved. However, where a liquid drain trap is used, the pressure acts on the underside the drain valve. This can lead to the build-up of excessive pressure within the drain, which may in itself be problematic for correct drain function, and which can in turn cause the drain valve to deform and/or become unseated, thereby preventing correct operation once the back-pressure is relieved.